This research program deals with basic mechanisms for regulating activities of genes. Its significance for human health relates to the requirement for broad and fundamental understanding of transcription mechanisms and their associated protein-nucleic acid interactions as the basis for precise and specifically targeted therapeutic interventions in gene expression. The proposed research analyzes transcription and transcriptional regulation in the archaea. Archaea are prokaryotes, like bacteria. The appreciation that they have a very special significance for understanding universal aspects of transcription mechanism is based on only recently acquired information, which specifies that archaeal transcription and gene regulation systems are hybrids of bacterial and eukaryotic components: their polymerases and core transcription factors are organized along eukaryotic lines, and many archaea possess histones, another eukaryotic "hallmark," while their transcriptional regulators appear to be of bacterial type. It is this combination of elements commonly regarded as mutually exclusive that promises unifying insights into fundamental transcription mechanisms. The following principal lines of research on archaeal transcription, transcriptional regulators and chromatin are proposed: one group of projects deals with the internal structure of archaeal RNA polymerase transcription complexes. Protein-nucleic acid contacts in different functional forms of these complexes will be mapped to answer specific questions about promoter recognition, polymerase recruitment, promoter opening and transcript elongation. Specific projects on archaeal histones focus on their effects on initiation and on whether they impede elongation of transcription. The effects of transcription elongation factors on RNA chain elongation and termination in the presence and absence of histones will also be examined. An additional group of projects on transcriptional regulators places its emphasis on two therrnostable archaeal homologues of broad-range (positive and negative) bacterial transcriptional regulators. Specific projects deal with the structures of complexes of these proteins with their own promoters, their effects on transcription and their competition with histones in modulating transcription.